Drawing machines are known, for metal products such as solid or tubular bars, which comprise a drawing assembly provided with two tracks, counter-rotating and opposite each other with respect to a drawing axis.
Each track includes a plurality of meshes constrained to each other in sequence, on each of which a drawing clamp is mounted which, during use, presses on at least one bar subjected to drawing.
In particular, each drawing clamp of one track cooperates with a corresponding drawing clamp present on the opposite track, in order to clamp the bar subjected to drawing from opposite sides, on a segment thereof which has already been drawn.
Each track is closed in a ring around a support plate and is made to rotate continuously by toothed wheels, generally two, one drive wheel and one driven wheel, mounted on opposite ends of the same support plate.
It is known to interpose an intermediate chain, of the type with rollers, between the support plate and the corresponding track, with the function of reducing friction between the meshes of the track and the support plate, introducing a rolling friction between these two components.
It is known that intermediate chains are normally idle and receive their motion from the tracks due to the effect of the contact with the meshes of the tracks. Generally, intermediate chains consist of meshes connected to each other with a desired play that allows to prevent the movement of the intermediate chains from blocking.
It is also known that intermediate chains are subjected during use to considerable wear, and to elongation due to the mechanical dilation of the various plays between the meshes that make up the chains.
As time goes on, this elongation becomes considerable, and can compromise the correct functioning of the intermediate chains, and also of the tracks in their entirety; it is therefore necessary to intervene to restore initial conditions.
To do this, it is necessary to cancel in the intermediate chains the effect of the mechanical dilation on the entity of overall play, by tensioning the intermediate chains themselves.
One disadvantage of known drawing assemblies is that they provide that the tensioning of the intermediate chains is carried out manually by a suitable operator; this means that the drawing machine must be stopped, and the operation in any case is imprecise and not effective.
Another disadvantage of known drawing assemblies is that identifying a condition of excessive elongation is based exclusively on the experience of the operator; it may therefore not be made at the best time, for example too early or too late. This second situation can determine a risk for the mechanical integrity of the intermediate chains, and also of the whole drawing assembly.
One purpose of the present invention is to obtain a drawing assembly for drawing machines in which the intermediate chains between the counter-rotating tracks and the support plates are automatically tensioned during functioning.
Another purpose of the present invention is to obtain a drawing assembly for drawing machines which allows to maintain a constant tensioning of the intermediate chains by means of continuous tensioning during functioning.
Another purpose of the present invention is to perfect a method for automatically and continuously tensioning the intermediate chains.
Another purpose of the present invention is to obtain a drawing assembly for drawing machines in which the condition of excessive elongation of the intermediate chains is identified and possibly signaled automatically, repeatably and effectively.
The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.